The invention concerns a process for increasing the heating value of fuel gas mixtures containing hydrogen by the conversion of said hydrogen.
Gas mixtures containing hydrogen may be the main products or by-products of chemical conversion processes, such as, without limitation, processes for the conversion of solid or liquid fuels and such mixtures may be of different or varying compositions. Such gas mixtures are, however, normally not fit for public gas supplies, as their composition and therefore their heating value, their Wobbe index and their density would normally not be in accordance with the standards and the codes of practice for gas properties ("Technische Regeln fur die Gasbeschaffenheit"). The higher heating value, the Wobbe index and the specific gravity of hydrogen-rich gas mixtures are considerably lower than the higher heating value, the Wobbe index and the specific gravity of town gas for which the following minimum values have been set in the code of practice mentioned hereinabove:
H.H.V.=17.58 MJ/m.sup.3 (n) PA1 Wobbe index (higher heating value divided by square root of density)=23.86 PA1 specific gravity=0.4
Known processes exist for the conversion of gas mixtures which do not conform to standard specifications, such as, without limitation, hydrogen-rich gas mixtures, into gases having such standard specifications. Such processes include processes for the removal of undesirable constituents, processes for adding desirable constituents and the process of methanation where the constituents of the gas mixture are converted by reactions represented by the following equations: EQU CO+3H.sub.2 .fwdarw.CH.sub.4 +H.sub.2 O (1) EQU CO.sub.2 +4H.sub.2 .fwdarw.CH.sub.4 +2H.sub.2 O (2)
For the known process of methanation, the gas mixture must therefore contain adequate shares of carbon monoxide and/or carbon dioxide, as are normally contained in such gas mixtures. Apart from the contraction in volume causing 4 and 5 parts of carbon monoxide and carbon dioxide respectively and one part of hydrogen to contract to one part of methane in the methanated gas (following the removal of the water formed during the reaction), the major disadvantage of said process of methanation is the fact that methanation is an exothermal reaction giving off considerable heat of reaction, such heat of reaction totalling 220.65 KJ/gmol for equation (1) above and 182.77 kJ/gmol for equation (2) above, so that approximately 20% of the enthalpy of the reacting gases is converted into heat of reaction which can normally only partly be used in other processes, such as the production of saturated steam which may be used for the generation of electric power. If saturated steam produced is used for electric power generation by means of a turbine generator, the efficiency of said use of said heat of reaction may range between 20 and 25% depending on the size of the installation, while more than 15% of the enthalpy of the reactants is lost.